/Engine/Source/Editor/UnrealEd/Public/ImportUtils/StaticMeshImportUtils.h
Simply put an AABB around mesh and use that to generate centre and radius. It checks that the AABB is square, and that all vertices are either at the centre, or within 5% of the radius distance away.
namespace StaticMeshImportUtils { bool StaticMeshImportUtils::AddSphereGeomFromVerts ( const [TArray](API\Runtime\Core\Containers\TArray)< FVector3f > & Verts, [FKAggregateGeom](API\Runtime\Engine\PhysicsEngine\FKAggregateGeom) * AggGeom, const TCHAR * ObjName ) }